Route exec-server HTTP through configured proxy policy (#35023)

## Why

Delegated HTTP requests need to honor the same outbound proxy policy as the
Codex process that starts the exec server.

## What changed

- Pass the configured `HttpClientFactory` through local and remote exec-server
  startup and use route-aware client pools for delegated HTTP and local MCP
  requests.
- Preserve per-request timeouts and follow-or-stop redirect behavior while
  keeping request URLs and sensitive response headers out of diagnostics.

## Testing

- Cover configured system-proxy routing across the exec-server transport.
- Cover both redirect policies and verify that success and failure logs do not
  expose request or response secrets.

GitOrigin-RevId: 4af6aec1d265c4db62dfcb6e1fb076fb31736137

codex-rs/exec-server/testing/exec_server.rs

@@ -5,6 +5,8 @@
 //! helper mode because sandboxed process requests re-exec this binary.
 
 use codex_exec_server::ExecServerRuntimePaths;
+use codex_http_client::HttpClientFactory;
+use codex_http_client::OutboundProxyPolicy;
 #[cfg(unix)]
 use std::ffi::OsStr;
 
@@ -26,5 +28,10 @@ async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
     let current_exe = std::env::current_exe()?;
     let runtime_paths =
         ExecServerRuntimePaths::new(current_exe, /*codex_linux_sandbox_exe*/ None)?;
-    codex_exec_server::run_main("ws://127.0.0.1:0", runtime_paths).await
+    codex_exec_server::run_main(
+        "ws://127.0.0.1:0",
+        runtime_paths,
+        HttpClientFactory::new(OutboundProxyPolicy::ReqwestDefault),
+    )
+    .await
 }